On Sat, 6 Sep 1997 08:43:25 +0100 "Ian White, G3SEK"
<G3SEK@ifwtech.demon.co.uk> writes:
>George T. Daughters wrote:
>>2: wouldn't a DC power supply like those used for
>>computers be a good filament source? with a little
>>tweaking and/or modification they could be set to
>>the factory's recommended voltage, and they would
>>act as a current source (at the limiting value for
>>the supply) and as the filament heated up, they
>>would change over to a regulated voltage. or is
>>the noise output of such a (typically switching)
>>supply just asking for another set of annoyances
>>when in receive mode? (even if we have the "perfect"
>>amplifier, we probably want to receive at least
>>*some* of the time!)
>
>A number of VHF mountain-toppers are using modified computer
>switch-mode
>supplies for 6V heaters, to avoid problems with generator sags and
>surges. Apparently the fully-enclosed and filtered units work well,
>but
>I'm sure an open-frame or unfiltered switcher would be a disaster on
>receive. Also, this is information relates to VHF - suppression of
>switching transients may not be so good at HF.
>
>Bottom line: it's worth a try.
>
>73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
Been up on the tower most of the day so missed the beginning of this.
I would be a bit cautious about using with directly heated filament
tubes Ian. My primary concern is with HV insulation breakdown. A properly
spec'd 5V 30A fil xfmr is designed with 5KV or more insulation and will
not place the HV out on the AC mains in case of a catastrophic tube
failure, etc. A switcher does not have that level of insulation. I have
looked at several switchers ( 5V 30A are cheaper than a standard xfmr for
crying out loud!) and decided the risk was not worth it.
Even 811A's at 1500V may be a safety issue. I prefer to err on the safe
side.
73....Carl KM1H
73...Carl KM1H
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